Adult extrarenal Wilms tumor occurring in the uterus.

Five previous cases of extrarenal Wilms tumor (EWT) occurring in the uterus have been reported. The oldest patient was 22 years. We report a case of uterine EWT occurring in a 42-year-old woman. Histologically, there was typical triphasic differentiation, including epithelial, blastemal, and mesenchymal elements. The important differential diagnosis in this age group, the malignant mixed mullerian tumor, is excluded by the absence of glomeruloid structures and primitive tubules. The exact histogenesis of EWT is unknown but most likely relates to the presence of nephrogenic rests occurring in the female genital tract.